function YYYYMMDDstart_day() {
    MonHead = [31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31];
    //先给年下拉框赋内容
    var y = new Date().getFullYear();
    var month = new Date().getMonth() + 1;
    for (var i = 2016; i < (y + 1); i++) //以今年为准，前30年，后30年
        document.reg_testdate_day.YYYY.options.add(new Option(" " + i + " 年", i));

    //赋月份的下拉框
    for (var i = 1; i <= month; i++)
        document.reg_testdate_day.MM.options.add(new Option(" " + i + " 月", i));

    document.reg_testdate_day.YYYY.value = y;
    document.reg_testdate_day.MM.value = new Date().getMonth() + 1;
    var n = MonHead[new Date().getMonth()];
    if (new Date().getMonth() == 1 && IsPinYear(YYYYvalue)) n++;
    writeDay(n); //赋日期下拉框Author:meizz
    document.reg_testdate_day.DD.value = new Date().getDate();
}

if (document.attachEvent)
    window.attachEvent("onload", YYYYMMDDstart_day);
else
    window.addEventListener('load', YYYYMMDDstart_day, false);

function YYYYDD(str) //年发生变化时日期发生变化(主要是判断闰平年)
{
    var MMvalue = document.reg_testdate_day.MM.options[document.reg_testdate_day.MM.selectedIndex].value;
    if (MMvalue == "") {
        var e = document.reg_testdate_day.DD;
        optionsClear(e);
        return;
    }
    var n = MonHead[MMvalue - 1];
    if (MMvalue == 2 && IsPinYear(str)) n++;
    writeDay(n)
}

function MMDD(str)   //月发生变化时日期联动
{
    var YYYYvalue = document.reg_testdate_day.YYYY.options[document.reg_testdate_day.YYYY.selectedIndex].value;
    if (YYYYvalue == "") {
        var e = document.reg_testdate_day.DD;
        optionsClear(e);
        return;
    }
    var n = MonHead[str - 1];
    if (str == 2 && IsPinYear(YYYYvalue)) n++;
    writeDay(n)
}

function writeDay(n)   //据条件写日期的下拉框
{
    var e = document.reg_testdate_day.DD;
    optionsClear(e);
    for (var i = 1; i < (n + 1); i++)
        e.options.add(new Option(" " + i + " 日", i));
}

function IsPinYear(year)//判断是否闰平年
{
    return (0 == year % 4 && (year % 100 != 0 || year % 400 == 0));
}

function optionsClear(e) {
    e.options.length = 1;
}